By way of example, within the scope of therapy planning in particle radiotherapy, an irradiation plan that defines control parameters for irradiating an examination object is created in advance. The irradiation plan is used to plan the irradiation of an object in accordance with specific prescriptions (e.g., target volume or dose distribution).
Particle radiotherapy is a well-established method by which, in particular, tissue afflicted by tumor diseases is irradiated. In the case of particle radiotherapy, charged particles, such as, e.g., electrons, protons, or carbon ions or other ions, or else photons or neutrons, are accelerated to high energies, shaped to make a particle beam and conveyed via a high-energy transportation system to one (or more) irradiation rooms. The target volume of the treatment object is irradiated by the particle beam in an irradiation room, wherein tissue outside of the target volume is necessarily also irradiated.
If accelerators with an active energy variation are used in particle radiotherapy, particle beams with different energies are used for irradiating the target volume. This leads to the formation of so-called isoenergy layers that may lie within, and outside of, the target volume. In an isoenergy layer, the particle beam applies particles with the same energy such that the particles of the particle beam to be positioned on the respective isoenergy layer respectively have an energy that differs from the energy of the particles for other isoenergy layers. Here, where possible, all particles for an isoenergy layer are applied with the aid of one spill (e.g., by a single accelerator fill) since loading or generating a new spill takes a number of seconds. In total, the interruption time for generating a new spill takes up a significant portion of the overall irradiation duration, depending on the number of particles to be applied. In order to provide a patient-friendly irradiation that is as short as possible, an accurate application of the dose in the target volume and the most economical operation of the particle irradiation unit are possible, it is necessary to keep the direct irradiation time (e.g., the time during which the patient is in fact exposed to the particle beam) and the overall irradiation duration (e.g., the time that the patient spends in the irradiation room) as short as possible. However, in so doing, it is necessary to consider the quality of the irradiation plan, which is ultimately to be assessed by the treating medical practitioner.